Embodiments of the present invention relates to the field of high-voltage engineering, in particular to supplying the high voltage required for operation to an X-ray tube. In particular, embodiments of the present invention relates to the non-destructive material testing by means of X-radiation, which can be generated, in particular, by means of microfocus X-ray tubes. In particular, the invention further relates to the electrically conductive connection between a high-voltage source and the acceleration section of an X-ray tube, in particular a microfocus X-ray tube, for applying the required accelerating voltage, which is typically between 50 and 350 kV in the field of material testing, to the acceleration section of the X-ray tube. In particular, the invention further relates to a high-voltage resistant cable for connecting a high-voltage source with the acceleration section of an X-ray tube, an equally high-voltage resistant plug as well as an equally high-voltage resistant socket. Further, it relates to a high-voltage resistant plug-and-socket combination, a high-voltage resistant connecting cable and an use of the aforementioned components. Finally, embodiments of the present invention relate to a testing assembly comprising an X-ray tube and a high-voltage source and to a method for reducing flashover-related damage during the operation of such an assembly.
The use of X-radiation for non-destructive material testing has been known for a long time in the prior art. The methods commonly used at the time this application was filed are generally transmission methods in which a shadow of the test object to be inspected is generated. The point of incidence of a high-energy electron beam on an anode serves as the X-ray source. This focal spot constitutes an approximately point-shaped source of X-radiation. The anode is generally a target of a suitable metal, such as copper or tungsten, for example, which can be cooled and, if necessary, also be configured to be movable, in particular rotatable. Basically, two types of X-ray tubes are commonly used in material testing. On the one hand, rotating anode tubes in which a rotatably mounted anode plate is disposed in an evacuated and sealed-off glass container are often used. Due to mechanical tolerances of the mounting of the anode, which were so far impossible to avoid, a movement of the focal point on the rotating anode inevitably occurs during the rotation of the rotating anode. This movement of the X-ray source relative to the stationary test object constitutes a substantial limitation of the resolution attainable by means of such a rotating anode tube.
A significant improvement of the resolution can be obtained with so-called microfocus X-ray tubes, which gained currency in recent years in the field of non-destructive material testing. Generally, microfocus X-ray tubes are characterized by a stationary target on which a highly focused electron beam is incident. An electron-optical system such as is known from the field of electron microscopy is used for focusing the electron beam. Due to the high degree of focusing of the electron beam and the fact that the anode is stationary, it is possible to generate an approximately point-shaped focal spot whose position relative to the test object is virtually stationary. Here, relevant positional changes substantially occur only due to vibration and, in particular, thermal drift of the X-ray testing system.
In contrast to fine-focus rotating anode X-ray tubes, microfocus X-ray tubes are generally not accommodated in sealed-off evacuated glass containers, but are rather disposed in a high vacuum-tight housing which can be opened for maintenance purposes, e.g. for replacing the anode material. Returning such a microfocus X-ray tube to operation after opening the high-vacuum housing requires the reestablishment of a high to ultrahigh vacuum. An insufficient vacuum results in the occurrence of flashovers upon application of the high voltage to the acceleration section of the electron beam source. They can also be caused by the occurrence of deposits on surfaces of the current-carrying parts, as they are inevitably present particularly after opening such an X-ray tube. However, deposits on the surfaces of current-carrying parts, which can result in the occurrence of flashovers, generally also arise during operation of a microfocus X-ray tube after a certain operating time. In order to return to operation a microfocus X-ray tube which has been exposed to ambient conditions, it is therefore necessary to carry out an elaborate conditioning process by means of which the current-carrying surfaces of the microfocus X-ray tube are freed from contamination and smoothed. Similar conditioning methods are also applied if deposits resulting in flashovers have formed during operation.
In practice, it is observed that the above-described flashovers between the cathode and the anode of the X-ray tube can lead to transient interference signals that can run from the X-ray tube to the high-voltage source and damage both the high-voltage source as well as the HV connecting cables used for the connection of the high-voltage source with the X-ray tube, because the transient interference signals can be very high-energy. These interference signals must be taken into consideration when designing the high-voltage source and the HV connecting cables used, which results in increased costs. In any case, they constitute an influential factor that is critical for the lifetime of the high-voltage source and electrical HV connecting cables used.
Therefore, attempts are being made in practice to reduce the occurrence of the aforementioned flashovers as far as possible by means of a suitable design of the X-ray tube. In particular, a surface treatment of the current-carrying parts of the X-ray tube has proved its worth in this respect, in which the surface roughness is reduced as far as possible, for example by high-gloss polishing of the metallic parts. In practice, however, this was found to require much effort; in particular, longer-term operation of such an X-ray tube may require an appropriate finishing of surfaces. It was also found in practice that such a surface treatment is not suitable for preventing the occurrence of flashover in principle.
This is where the invention comes in, which has set itself the object of indicating specific measures for effectively protecting the high-voltage source used as well as the HV connecting cable used for connecting the high-voltage source to the X-ray tube against damage from flashover-related transient interference signals.